Earlier this year Renault were rumoured to be suffering financially. With Senna at the team, four new sponsors come along. http://www.f1fanatic.co.uk/2011/09/07/senna-helps-renault-add-sponsors/ It's very possible that when Boullier was faced with the choice of Heidfeld or Senna, he chose Senna's money over Heidfeld's consistency and leadership.
The sponsor deals are very minor in F1 terms. Petrov brings much more dosh to the team. Also Senna comes with a bit of talent which Heidfeld nolonger had
Yes he scored a whole two more points than Petrov True leadership. as was his 8-2 Qualifying deflict to Vitaly. Sarcasm over, there is no way Petrov has improved that much since last year. It is not that Nick did badly. More that he just failed to live up to expectations and with no future in him why not give Senna his chance (not that the sponsors dont sweeten the deal).
Yeah fair enough, I think people expected him to be as good as Kubica was, which he isn't, added to Petrov's improvement the gap is a lot smaller than Renault would have wanted. Plus, I don't think Eric liked Heidfeld much
